U.S. Pat. No. 4,398,817 shows a magnetic brush toning apparatus for applying either of two toners to an electrostatic image with the same applicator. The toners are contained in storage means around a rotary applicator. When the applicator is rotated in a clockwise direction a first developer is moved directly from its storage means through a toning zone and then is stripped off the applicator and returned by a complicated return mechanism around the other storage means to its original storage means. When the applicator is turned in a counterclockwise direction toner is moved from the second storage location past the toning zone and is stripped and returned through a second return path around the first developer storage means to its correct storage means.
According to this patent, this structure permits toning an electrostatic image with either of two different colored toners with a single applicator. However, the structure requires an elaborate return mechanism for spent developer to prevent it from falling into the storage location for the other color developer.